A number of standard mobile communications systems are currently under development. For example, in Europe the GSM900 system operating at 900 MHz is gaining wide acceptance while in North America the near equivalent PCS1900 system is a current standard operating at 1900 MHz. Within each of these systems a set of standard operating procedures has evolved, and all equipment supplied for use in such a system must conform to the corresponding standard. This provides a significant advantage to the system operator as he can obtain equipment from a number of suppliers and be confident that it will be fully compatible. For example, the operator may purchase handsets from one manufacturer, base stations from another and mobile switching centres from a third. Although this provides the operator in that he can force down the costs of the purchased equipment, there are attendant disadvantages.
Firstly, the key protocols defining the standard must be conceived at the original installation of the system. If these protocols have not been chosen with sufficient care and forethought, adherence to the standard can preclude the adoption of more advantageous techniques that may subsequently become available. Secondly, although the key protocols may be defined, there is often considerable scope for the provision of proprietary services that can provide added value to a particular manufacturer's product. This provides the operator with the problem of supporting different equipment designs. In practice a particular operator supports only one service mix and users of equipment, e.g. handsets, capable of providing other services may well find that those services are not supported. Thirdly, there is increasing concern about the proliferation of base station installations that are required to service a variety of mobile communications systems that are operating in the same geographical region and there is thus a need to minimise the number of such installations.